An infrastructure-based wireless network typically includes a communication network with fixed and wired gateways. Many infrastructure-based wireless networks employ a mobile unit which communicates with a fixed base station that is coupled to a wired network. The mobile unit can move geographically while it is communicating over a wireless link to the base station. When the mobile unit moves out of range of one base station, it may connect or “handover” to a new base station and starts communicating with the wired network through the new base station.
In comparison to infrastructure-based wireless networks, an ad hoc network typically includes a number of geographically-distributed, potentially mobile units, sometimes referred to as “nodes,” which are wirelessly connected to each other by one or more links (e.g., radio frequency communication channels). The nodes can communicate with each other over a wireless media without the support of an infrastructure-based or wired network. Links or connections between these nodes can change dynamically in an arbitrary manner as existing nodes move within the ad hoc network, as new nodes join or enter the ad hoc network, or as existing nodes leave or exit the ad hoc network. Because the topology of an ad hoc network can change significantly techniques are needed which can allow the ad hoc network to dynamically adjust to these changes. Due to the lack of a central controller, many network-controlling functions can be distributed among the nodes such that the nodes can self-organize and reconfigure in response to topology changes.
One characteristic of the nodes is that each node can directly communicate over a short range with nodes which are a single “hop” away. Such nodes are sometimes referred to as “neighbor nodes.” When a node transmits packets to a destination node and the nodes are separated by more than one hop (e.g., the distance between two nodes exceeds the radio transmission range of the nodes, or a physical barrier is present between the nodes), the packets can be relayed via intermediate nodes (“multihopping”) until the packets reach the destination node. As used herein, the term “multihop network” refers to any type of wireless network which employs routing protocols among nodes which are part of a network. In such situations, each intermediate node routes the packets (e.g., data and control information) to the next node along the route, until the packets reach their final destination
The Institute of Electrical and Electronics Engineers (IEEE) 802.16 refers to a set of IEEE Wireless Local Area Network (WLAN) standards that govern broadband wireless access standards. IEEE 802.16 standards have been and are currently being developed by working group 16 of the IEEE Local Area Network/Metropolitan Area Network (LAN/MAN) Standards Committee (IEEE 802). Any of the IEEE standards or specifications referred to herein may be obtained at http://standards.ieee.org/getieee802/index.html or by contacting the IEEE at IEEE, 445 Hoes Lane, PO Box 1331, Piscataway, N.J. 08855-1331, USA. The IEEE 802.16 Working Group on Broadband Wireless Access Standards aims to prepare formal specifications for the global deployment of broadband Wireless Metropolitan Area Networks. Among other things, the 802.16 standards define a point-to-multipoint (PMP) system with one hop links between a base station and a subscriber station. Such network topologies sometimes include pockets of poor coverage areas. While such coverage voids can be avoided by deploying base stations in a dense arrangement, this drastically increases both the capital expenditure (CAPEX) and operational expenditure (OPEX) for the network deployment. A cheaper solution is to deploy relay stations (also known as relays or repeaters) in the areas with poor coverage. These relay stations can repeat transmissions from the base station so that subscriber stations within communication range of a relay station can continue to communicate with the base station using high data rate links. The incorporation of relay stations in an IEEE 802.16 network transforms it into a multihop network with each node having one or more options to access a network, such as the Internet, via a base station.
For example, networks which comply with the IEEE 802.16j specifications will employ relay stations in an IEEE 802.16e network to provide for range extension and capacity improvements. Depending upon the particular network configuration, a particular subscriber station may gain network access via one or more neighbor relay stations and/or one or more neighbor base stations. In addition, relay stations themselves might have one or more available path options to connect to a particular base station. The relay stations can be implemented such that they are fixed, stationary, nomadic or mobile. The IEEE 802.16j standard requires that the air interface link between a relay station and a subscriber station appears to be exactly like the air interface between the base station and the subscriber station. From the perspective of the subscriber station any communications with the base station which are relayed through the relay station appear to be the same as if they had come directly from the base station.
Many wireless networks implement Automatic Repeat-reQuest (ARQ) methods for resolving errors that can occur during data transmission. These ARQ methods are usually implemented in the Data Link Layer or Transport Layer of the Open Systems Interconnection (OSI) model. Most ARQ methods use acknowledgment (ACK) messages, negative acknowledgement (NACK) messages and timeouts to achieve reliable data transmission. For instance, in one basic ARQ method, when a destination node receives a packet, the destination node sends an acknowledgment (ACK) message to a source node to indicate that the destination node has correctly received a data frame or packet. The ACK message allows the physical layer to know whether the data payload has been successfully delivered. Some ARQ methods also implement a Negative Acknowledgment (NACK) message that a destination node can transmit to the transmitter when the destination node has detected a problem with the data payload. In cases where the source node does not receive any response from the destination node (e.g., the destination node fails to receive anything from the source node and therefore does not transmit and ACK or NACK), the source node can assume there was a problem with the data payload (e.g., a lost packet). As such, if the source node does not receive an ACK or NACK within a certain amount of time (i.e., during a “timeout period”) after it sends a data message (i.e. such as a frame/packet), then the source node will repeat or re-transmit the message and wait for an ACK. The source node typically continues to re-transmit the message until it receives an ACK message is received or a predefined number of re-transmissions is exceeded.
In a multihop network that implements relay stations, such as those described above including those that comply with IEEE 802.16j specification, it is difficult to use conventional ARQ methods. For instance, a publication entitled “An ARQ scheme for IEEE 802.16j multihop relay networks,” Peng Yong Kong et al., Nov. 7, 2006, describes application of conventional ARQ methods to a multihop cooperative relay network. According to this ARQ method, when a base station transmits a data frame/packet to multiple relay stations, each of the relays stations sends ACK/NACK message to the base station. This approach can flood the air interface with ACK/NACK messages.
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The apparatus and method components have been represented where appropriate by conventional symbols in the drawings, showing only those specific details that are pertinent to understanding the embodiments of the present invention so as not to obscure the disclosure with details that will be readily apparent to those of ordinary skill in the art having the benefit of the description herein.